1. Field of the Invention
The present invention relates generally to a circuit for generating a system clock signal. More specifically, the present invention relates to a digital decoder circuit for receiving an input digital signal which includes data and a range tone signal and then providing a clock signal which is phase locked to the range tone signal.
2. Description of the Prior Art
Targets are used by the military services to allow military aircraft, ships and other weapons systems to practice in a real life environment without risking injury to human or the loss of expensive and sophisticated equipment. Each target, in turn, includes a target transponder receiver for receiving and processing video data which controls the movement of the target based upon the information provided by a ground station, an ocean going vessel or the like.
One particular type of target transponder receiver is a Model No. AN/DKW3 Target Transponder Receiver used in military targets. The AN/DKW3 Target Transponder Receiver includes a decoder subassembly/module which receives a video input signal having Manchester coded data bits and a range tone component having a frequency of about 102.6 kilohertz. The decoder subassembly upon receiving the video input signal processes the video input signal converting the Manchester coded data bits to digital data. The decoder subassembly also provides a system clock signal phase locked to the range tone component of the video input signal as well as a synchronized four phase clock signal which is used by the AN/DKW3 Target Transponder Receiver to further process the received information.
The decoder subassembly (illustrated in FIG. 1 as a block diagram) presently used in the AN/DKW3 Target Transponder Receiver is complex in design having numerous electronic components which are susceptible to failure and therefore expensive to repair or replace.
With these and other disadvantages of the prior art decoder circuit, the present invention was conceived and one of its objects is to provide a relatively simple yet highly efficient electronics decoder circuit which will phase-lock to the range tone component of the video input signal to generate a system clock signal.
It is another object of the present invention to provide a logic signal which indicates the presence of the range tone component of the video input signal.
Various other advantages and objectives of the present invention will become apparent to those skilled in the art as a more detailed description of the present invention is set forth below.